One of the most commonly performed invasive procedures in modern medicine is the insertion of an intravenous (IV) or arterial catheter. However these procedures require substantial skill for success, and even experienced and skilled practitioners have exhibited significant failure rates. This results in considerable pain and anxiety for the patient, who may have to endure multiple attempts to insert the catheter. Experienced clinicians report that nearly every patient they encounter vividly recalls having suffered failed IV or arterial insertions in the past.
Most insertion failures appear to occur at a discrete point in this multi-step procedure. That is, the attempt to thread the catheter after the vessel has been punctured by the needle, and flashback of blood has occurred. Beginners often fail to appreciate that when the flashback of blood occurs for the clinician to observe, the needle tip (and orifice) are in the vein or artery, but the catheter tip, which overlies the needle, has not yet entered the vessel. Rather, the catheter tip may still be proximal of the vessel. This is because blood begins to enter the needle lumen under pressure (and hence flashes back at the proximal end of the needle) as soon as the needle lumen is placed in fluid communication with the bloodstream.
By way of further illustration of this undesirable outcome, reference is made to FIG. 1, which depicts a typical needle and catheter arrangement 100 according to the prior art. The arrangement 100 includes a hollow metallic (typically surgical stainless steel) insertion needle 110 with a lumen 112 of appropriate size/diameter for the blood vessel 120 into which it is inserted (For example, needle sizes 14 gauge (G), 16 G, 18 G, 20 G, 22 G or 24 G). The distal end of the needle includes a conventional sharp, beveled, chisel-like tip 114 with an open orifice 116 that extends proximally into the lumen directly from the angled cylindrical orifice edge. This tip includes a distal point 118 that is quite sharp and enables piercing of the skin layer 122 and vascular wall 124 as shown with minimal discomfort for the patient. Overlying the needle 110, proximal of the tip 114 is a closely conforming catheter 130 constructed from a biocompatible polymer of conventional design. The distal end 132 of the catheter ends proximally of the angled tip 114, forming a small-diameter step that normally passes into the puncture hole created by the tip 114. The proximal end of the arrangement 110 typically includes an assembly with a distal portion that defines a fitting 142 interconnected with the catheter 130 and a proximal portion 144 that is interconnected with the needle. The two portions 142 and 144 can be withdrawn axially from each other so as to withdraw the needle 110 proximally from within the catheter lumen, while maintaining or advancing the catheter 130 distally with respect to the vessel 120 so as to thread and implant the catheter fully into the vessel.
As shown in FIG. 1, the needle tip 114 has been inserted by the clinician into the vessel 120 and the now-open path between a distal-most portion 150 of the tip orifice 116 and the bloodstream causes the flashback of blood through the needle lumen 112, which is visible in a flash chamber 160 at the proximal end. However no portion (or substantially no portion) of the catheter's distal end 132 has entered the vessel 120. Thus, an inexperienced or inattentive clinician may attempt to thread the catheter immediately upon such flashback. This premature threading generally causes the clinician to blow the insertion, because the catheter tip 132 pushes the pliant vessel 120 away from, and off of, the needle as the catheter is driven distally in an attempt to implant it in the vessel.
More experienced practitioners, conversely, are aware that, following flashback, the entire needle/catheter arrangement 100 should be inserted an additional 2 mm (more or less) before catheter threading is attempted. Unfortunately, as shown in FIG. 2, during this additional-distance insertion, the sharp, beveled point 118 on the distal tip of the needle 110 often penetrates the opposite or back wall 210 of the vessel 120 resulting in failure and a painful hematoma.
U.S. Pat. No. 5,649,911, entitled INTRAVENOUS CATHETER AND DELIVERY SYSTEM, by Trerotola provides a solid, beveled needle tip joined to a straight cylindrical body with a side hole proximally spaced from, but near the tip. The hole is carried on the needle body and the adjacent overlying catheter wall, near its distal end. This hole enables flashback to occur after the catheter has fully penetrated the vessel, so that it can be threaded without risk of non-penetration. However, the use of a solid tip dictates that the needle be inserted a significant distance into the vessel before any flashback occurs. This degree of insertion may, in fact be excessive. In addition, the tip is constructed with the traditional bevel, having a point residing in line with the sidewall. In other words, the tip and point are simply extensions of the bottom side of the cylindrical needle shaft, and thus the structure of the needle still invites over-insertion as set forth in FIG. 2 above. The risk of over-insertion is, in fact enhanced by the relatively proximal placement of the side hole. Moreover, the traditional beveled tip does nothing to reduce the damage potential from an over-penetrating insertion.
It is, thus desirable to provide an intravascular needle and catheter arrangement that provides flashback at the point in which the catheter is sufficiently inserted into the vessel. It is also desirable to provide a needle that reduces the risk of damage to the vessel from over-insertion of the needle.